This invention relates to counting system for radioactive fluids and, more particularly, to such systems adapted to analyze various fluids in a nuclear power plant during post accident conditions and/or normal operation.
Radioactively "hot" fluid samples from a nuclear reactor in the event of an accident usually affects the accuracy of the equipment used for analysis in the counting room during normal operation. Consequently, some type of on-line analyzing system is highly desirable for this purpose. Prior on-line systems for analyzing radioactive fluids in nuclear power plants typically use one or more of the following features: (1) a movable, variable collimator and a fixed sample position or multiple sample positions, (2) an uncollimated fixed sample position with a fixed geometry and variable source concentration and/or (3) uncooled, pressurized reactor coolant samples.
Variable collimation usually means a change in geometry and detector efficiency and variable sample positions or sample volume requires changes in geometry efficiency and/or the detector efficiency. These variables require special calibration techniques. Variable collimators are quite large and heavy. Since the area in which the counting system is located may be exposed to relatively high concentrations of radioactivity, prior on-line systems typically are power driven and at least partially automatic in order to protect the operator against the excessive radiation doses. Consequently, the resulting complex systems are relatively expensive and have low reliability.
While being transported to a sample station, high pressure, high temperature liquid samples, such as nuclear reactor coolant, tend to become cooled and degas to produce two-phase flow which affects accuracy of the measured radioactivity.